We have found that extremely short electric pulses in the nanosecond range (nsPEF) can be used to treat skin cancer in mice with striking results. When 300 pulses that are 300 ns in duration and 40 kV/cm in amplitude are applied to murine melanomas, the tumors regress by 90% within two weeks. If a second such treatment is applied at that time, the tumors can be completely eliminated. A total electric field exposure time of 1.8 microseconds causes these tumors to self-destruct. The mechanism does not involve hyperthermia because we have measured the temperature within the tumor during pulse application to increase no more than 3 oC. Two targets that we have identified are the cell nucleus and the tumor's blood supply. The tumor cell nuclei shrink to half of their original size within minutes after nsPEF application and the blood flow to the tumor is halted for about two weeks. We have been conducting a long-term study of 36 mice. While none of the 18 untreated control tumors exhibited complete remission, all of the 18 nsPEF-treated tumors exhibited complete remission without recurrence for at least 120 days. The rate of metastasis of melanoma cells to lung and liver was also much lower in nsPEF-treated mice that it was in controls. Here we propose to extend this therapy to investigate the effect of nsPEF on murine squamous cell carcinoma and determine the optimal pulse parameters to completely eliminate these tumors in mouse skin. We will also determine if nsPEF treatment reduces metastasis of melanomas that are treated with nsPEF when they have grown to 8 mm in diameter. We will also determine if nsPEFs are an effective treatment of a skin tumor that has arisen from native epidermal cells. Next we will identify the mechanisms by which nsPEF triggers tumor regression. We will investigate the role of reactive oxygen species because they can generate oxidative stress-induced DNA damage. We will also investigate the involvement of the apoptosis pathway since that can also lead to DNA fragmentation. This work should determine how useful this new technology will be in future treatments of skin tumors. If this approach can be reliably used to eliminate malignant skin lesions, it could offer a welcome, scar-free alternative to surgery that could improve the quality of life for hundreds of thousands of dermatology patients yearly. This research will explore a new type of cancer therapy in which skin tumors are treated with ultra-short electric pulses. This treatment instructs the tumor to self-destruct and stops blood flow to the tumor. This promises to become a scar-free therapy that could replace surgery and improve the quality of life for hundreds of thousands of dermatology patients treated for skin cancer each year.